While the faults were not thought to be weather related, EDF pleas to users to turn off their air conditioning to reduce pressure on the network while emergency repairs continued.

Earlier, furious traders along Oxford Street and Regent Street were forced to close when the shutdown wiped out tills, lighting and air-conditioning.

Oxford Circus Tube station, one of the busiest in London, was closed for almost an hour and a half and big name shops were among those forced to close temporarily.

Florence Torrens, head of communications and marketing at upmarket department store Liberty of London, in Regent Street, said: "All the systems went down. So many businesses and shops were affected in this area of central London."

The flagship Topshop store in Oxford Circus closed at 6pm, three hours earlier than usual because of the disruption, a spokeswoman said.

Jace Tyrrell, spokesman for the New West End Company which represents businesses on Oxford Street and Regent Street, said it was too early to say how much money had been lost to the power cuts.

"This is bad news for business and bad news for shoppers in the West End," he said.

"We are very disappointed on behalf of businesses. It is even more disappointing for shoppers who turn to stores to escape the heat."

The glitches, two at substations after a power cut on Sunday and two unrelated faults on underground cables, interrupted supplies to three separate blocks of EDF customers during the day yesterday.

About 760 power customers in one section bounded by Oxford Street and Regent Street were left without power between 10am and 2pm, at which point 1,300 premises found supplies cut until 6pm.

Last night a further 1,200 customers nearby lost supply until 7.30pm.

EDF said that it was working through the night to solve the problems but if it did not succeed the same pattern could be repeated today.

"We do understand how much disruption these interruptions have caused but stress this is a highly unusual sequence of faults and our emergency teams are doing everything possible to restore normal supplies as soon as they can," the company said.

It added: "The situation has been exacerbated by the high demand on our network caused by the continued hot weather.

"As a result we are appealing to all customers in this area to limit non-essential use of electricity during daytime hours."

The power cuts come just three days after EDF announced its second raft of price hikes this year.

From Monday it will charge 19 per cent more for gas and 8 per cent more for electricity - rising to 9.1 per cent for customers in its northern region.